diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index 403ca57f6011..d609ac3cb9a4 100644
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -664,8 +664,11 @@ static ssize_t clusterip_proc_write(struct file *file, const char __user *input,
 	char buffer[PROC_WRITELEN+1];
 	unsigned long nodenum;
 
-	if (copy_from_user(buffer, input, PROC_WRITELEN))
+	if (size > PROC_WRITELEN)
+		return -EIO;
+	if (copy_from_user(buffer, input, size))
 		return -EFAULT;
+	buffer[size] = 0;
 
 	if (*buffer == '+') {
 		nodenum = simple_strtoul(buffer+1, NULL, 10);